This invention relates to an infeed conveyor system for separating articles unit by unit or in groups of units. The new infeed conveyor system is illustrated herein in a special adaptation for separating rolls of bathroom tissue (BRT) and household paper towel (HHT) rolls from a nominally continuous supply of rolls preliminary to feeding them in units or groups to a wrapping machine.
Because of their delicacy, paper rolls are highly susceptible to being scuffed and to being dented or deformed as they transit an infeed conveyor system. Some prior infeed systems feed paper rolls singly or in groups from a first supply conveyor, where they are stationary or moving at a certain speed, to second conveyor on which they experience marked acceleration or deceleration. The feed from supply is customarily intermittent. The second conveyor usually has abrasive surfaces for developing the friction which is desirable to transport the rolls effectively. But, undesirably when the rolls undergo a speed change, relative motion between the rolls and the abrasive surfaces causes scuffing.
Squeezer conveyors are preferred for advancing rolls from a supply to a place where they are separated as units or in groups of two or four which is common for HHT and BRT. Squeezer conveyors are comprised of two spaced apart parallel belt loops between which a column of rolls fits snugly so that when the belts are translated, frictional engagement of the belts on the rolls will transport them along the belts. When operated in their prior art mode, they do impart a speed change to the rolls and scuffing results. In practice, the supply of rolls is interrupted occasionally in which case the squeezer conveyor may discharge all or many of its rolls, thus leaving no rolls between the belts or a gap between the last roll in the remainder of the column and the input end of the belts. Then when the supply is restored and the conveyor is started again the abrasive action and scuffing occurs because of the speed change as the rolls are fed in.
Another characteristic of infeed conveyors is that the separated rolls must be delivered from a separating device adjacent the output of a squeezer or other type of conveyor so they arrive in proper phase relationship with moving elements in receiving apparatus such as a bucket wheel, flight conveyor or elevator which transports roll units or groups to a wrapping machine. Generally, the rolls are gated intermittently at regular intervals and all parts of the machine are driven from a common source in an effort to maintain synchronism, that is, to establish a fixed time for rolls to travel from the gate to the receiving apparatus. Undesirably low speed and reduced productivity are consequences of operating in this mode.
U.S. Pat. No. 3,823,813 discloses a prior roll unit and group forming machine. It has a conventional supply conveyor belt 12 which delivers product, when available, to a gate 14 which is opened and closed cyclically with a fluid operated cylinder 156. The cylinder is switched on and off with a relay operated valve under the control of a cam driven switch 146. The cam is driven from the main shaft of the machine for synchronizing purposes. Product is cyclically gated onto an accelerating conveyor belt 30 which is driven at a uniform speed through a main shaft connection. The accelerating belt advances the product quickly away from the gate and into spaced apart guides or plates 50 and 52 which are aimed toward a flight conveyor which transports the rolls to a wrapping machine. The rolls are pushed along the guides with pusher bars that are carried on a chain and sweep endwise through the spaces between the guide plates. Some pressure rolls which cooperate with the accelerating belt conveyor, the accelerating belt, the pusher bar drive mechanism and the flight conveyor are all mechanically interconnected in an effort to maintain synchronism, that is, to assure that a fixed time will elapse between opening of the gate and arrival of the product at the proper time in the flight conveyor.
One of the disadvantages of a machine of the type shown in the patent is that gates 14 open and close every machine cycle to release product from the supply conveyor to the accelerating conveyor. Hence, the leading product on the supply conveyor and a backlog of product, which may extend 20 to 30 feet behind it, move while the gate is open and stop abruptly when the gate closes. The inertia of the backlog and the return force of the closing gate can deform or dent the lead roll at least.
As is evident, product flow from the supply to the accelerating conveyor is not continuous. The accelerating conveyor belt 30 and the cooperating pressure rolls in the prior machine are driven at a high lineal speed and the rolls have low speed because they are stopped prior to opening of the gate. They then undergo an abrupt increase in speed which can cause scuffing. In addition, limitations on practical gate operating speeds limit the speed of the entire machine to a relatively low speed.
If two lanes of product are being controlled by one gate for grouping pairs of products, one lane will inevitably run out of product, while the other presses against the gate. Lack of product in one lane would require the other gate to be held closed as long as the lack existed or incomplete groups of products would result. When product becomes available again, additional scuffing could take place as the gate moved to the side. No means of dealing with such problems is apparent in the patent.
As will be seen, in accordance with the present invention, flow from the supply conveyor to an accelerating conveyor is continuous by reason of interposing a variable speed high friction squeezer conveyor between these conveyors. When rolls are fed from two lanes and the supply in one becomes exhausted, both squeezer conveyors stop while still full of products. When product is restored, it strikes no gate but merely bumps into a soft roll which was left in the squeezer when it stopped. The new supply of products is brought to a stop only on a low friction supply conveyor by contact with prior products.
Gates, as in the prior patent, are operated with air cylinders having cams controlled by an air valve operated by a timing cam. If machine speed varies, timing of the gate must be changed to compensate for the cylinder operating at constant speed independently of machine speed. There is always a lag between opening of the cylinder valve by the timing cam and the time at which the gate should open. It is difficult to adjust for this variable. Repeatability and maintenance of synchronism is problematical with air operated devices at high machine cycling speeds so the machine may have to be run slower and lower productivity results.
Intermittently operated mechanisms such as the gates and air cylinders in prior machines cause vibration and noise which, it will appear, are obviated by the new continuous flow machine described herein.